Novak Djokovic says he is not concerned about his number one ranking as he returns to action after becoming a father for the first time.

The Serb, 27, plays his first match at the Paris Masters on Tuesday since wife Jelena Ristic gave birth to son Stefan.

Philipp Kohlschreiber is Djokovic's first opponent since he lost to world number two Roger Federer in Shanghai earlier this month.

"I feel like I'm already number one becoming a father last week," he said.

It is the first indoor tournament of the defending champion's season as the players prepare for the ATP World Tour Finals in London in November.

Federer is just 490 points behind Djokovic in the ATP world rankings, with the winner in Paris receiving 1,000 points.

"I never thought that he's not a competition for number one of the world," said Djokovic. "I always thought that he's one of the best players in the world, and he keeps on proving everybody that he deserves to be there.